Static Phase Converter?

JB, I'd say probably, errr welll, make that maybe. Do this: Get in touch with Phase-A-Matic, large maker of static phase converters. Be prepared to give them the name plate information from the motor.

Thank you for the advice, Robert.

Joe

I am pretty sure you would be content with the performance of a lathe at home with a 5 HP 3 phase motor powered with single phase. You probably wont be content with its performance if you intend to run it loaded over about 4 HP for extended periods. I'm impressed with the ability of a lathe like that being able to reverse quite quickly.

Jerry

Jerry,

Thanks for the help. I don't think I'll be loading it up over 4 HP, especially for long periods of time. My other concern is whether the two speed motor will work with a static converter. Some say yes, some say no and some say maybe.

Thanks again.

Joe...

Reversing could get interesting. That can put a lot of stress on a phase converter. I've had the situation where a small rotarty would reverse instead of the lathe, a situation that could really make your day.

You could get around this simply by pausing with the switch in the off position until the spindle stops, then applying the power in reverse, right?

Chris

True, but the value of instant reverse is lost. There are times when that feature is very valuable to the guy on the machine. Tapping a hole with a tap in the spindle comes to mind. Failure to reverse instantly could prove expensive.

Harold

The only 3 phase motor I've not been able to run on a properly sized static converter is the 2 speed motor on my Feeler HLVH clone. Whether this is due to something common to all 2 speed motors, or peculiar to this specific motor, I can't say.

Bob's suggestion to ask Phase-a-Matic is sound advice.

Another option is a VFD, which is what I did on my lathe.

Ned Simmons

My lathe also has a two-speed motor, rated at 5 HP on high speed and 3 HP on low speed. I could start it in either mode with a static converter -- but not with the same static converter, or at least not with the same capacitance.

There may be a way to trick a relay into the lathe's wiring so when the high-speed mode is engaged more capacitance is switched into the static converter.

Another option would be to manually switch the converter when you change speeds.

A large enough rotary converter, probably 10 HP idler, would start it in either mode.

you may find that a VFD costs about the same as a static converter (unless you happen to have the parts and plan on building it yourself) - look for a used one

You can build a 10 HP rotary phase converter for next to nothing, in a couple of days, see how I did it

I am using it very often these days. Works fine, unless it is overloaded, in which case it is merely mediocre.

With a static phase converter, you will not be able to realize the full nameplate power of the motor, may have problems reversing it, and it would run in an unbalanced mode.

Static phase converter is not really a phase converter, it is a starting circuit that spins up 3 phase motors and lets them run on single phase once they spin up.

i

Thus eliminating the "reverse it quite quickly" which was promised about four articles back-thread. :-)

If you want to do this, you want a hefty rotary phase converter. I don't think that a "static" phase converter as made by "Phase-O-Matic" could handle a two-speed three-phase motor very well. It will start well on one or the other speed, but not both.

Enjoy, DoN.

According to william_b_noble :

Hmm ... a VFD is not likely to work well with a two-speed three-phase motor -- unless you do all speed switching with the VFD. You're not supposed to put the switch between the VFD and the motor, as the voltage spikes from the switching can zap the output transistors of the VFD.

Here is a place where I feel that a rotary converter (build-it-yourself) would be the better choice. Or -- you could limit yourself to one set of windings on the motor, and do all speed changing with the VFD. For extreme cases (where you *really* need the higher torque of the low speed, or the higher speed of the high speed), you can stop the motor entirely (using the VFD's controls), switch to the other speed at the lathe's switches, and then start the motor back up with the VFD.

Good Luck, DoN.

I don't think that is the case. All 2 speed motors that I have looked at have a much lower HP rating on Low speed than high speed. Usually it is less than 1/2. I would venture that a 2 speed motor runing on high speed but slowed down with a VFD will actually have more (or at least as much) HP as the same motor runing on low speed.

So in my opinion you can wire the lathe to only use high motor speed and then use the VFD to generate the low speed without any loose in motor torque.

Once you use a VFD you will love it. For example I was facing an

8 inch diameter disc. I set the VFD for 20Hz and geared the lathe for the speed I wanted for full diameter. As the toolbit works it way towards the center, I gradually increase the VFD frequency to increase the spindle RPM. It makes facing a big object so much faster and better.

chuck

I run a 5 horse 2 speed as you are speaking of on a 7.5 horse rotary built from a phase-a-matic heavy duty static converter rated for 8 hp. It will NOT start the lathe on the low range but doesn't have any problems at all with the high range.

Yea, I know...I need bigger. I just wanted to throw out some numbers that may help. I would suspect that you will not get good service from a static converter alone. It may be "good enough" for light work in the speedier gear range but you'll have to seriously oversize it to go into the low range.

Koz

Or in at least one instance (mine), though the HP of both speeds is within the range of the static converter, the motor will not start or run properly on either speed.

Ned Simmons

I was able to keep all the original functions of the 2- speed motor on my lathe when I installed a VFD. The two speed select contactors are between the VFD and the motor windings, and work as they always have. The direction commands to the VFD come from the reversing contactor, which no longer has any direct connection to the motor.

The only thing I can't do (you *can*, but for the reason you mentioned, *shouldn't*) is switch from hi to lo on the fly, but that's not a problem now that speed is controllable with the VFD's speed pot. Most VFDs have a zero speed output, so it would be possible to prevent switching the speed select contactors unless the motor is stopped, but I didn't think it worth the trouble.

Ned Simmons

Rather than risk frying the old two speed motor on my TM mill, I got a

1 hp. Marathon inverter duty motor to go with the VFD. Good motors aren't that expensive, or find a used one. The VFD handles generating the low speed end well.

Pete Keillor